This invention relates to a braking system of a chain saw.
While a chain saw is in operation, an accident may happen involving the vigorous upward movement of a chain bar due to the resistance offered by the material being sawed (a kickback phenomenon) or the slipping of the hand of an operator from a handle to be caught in a saw chain. In order to prevent such accident, attempts have hitherto been made to devlop an efficient braking system effective to instantaneously interrrupt the operation of the chain saw when the aforesaid phenomenon occurs.
Such accident occurs unexpectedly and may cost the operator his life. Therefore, any braking system should be able to instantaneously apply the brake to the brake means to stop the sliding movement of the saw chain. There have hitherto been developed many types of braking system. For example, in one type of braking system widely used and known in the art as from U.S. Pat. No. 3,776,331, tilting of a sensing lever unlocks locking means, and permits a spring or other resilient means to interrrupt the rotation of a clutch drum of clutch means by its biasing force, thereby stopping the sliding movement of the saw chain which is driven by the clutch drum. This system is complex in construction and requires a large space for housing the brake mechanism. Also, transmission means for transmitting a force from the sensing lever to the brake mechanism is complex in construction. Thus the braking system described hereinabove has had disadvantages in that it takes time for the force exerted on the sensing lever to be transmitted to the brake mechanism, causing a delay in application of the brake, and that the braking force applied to the saw chain is determined by the resilient force of resilient means used in the chain saw.
When a chain saw is provided with a braking system, it has been popularly practiced to mount sensing lever means forwardly of a front handle for the convenience of applying the brake. This arrangement is rational. However, in view of the construction of a chain saw, this arrangement raises a problem with regard to the designing of a chain saw, because ports for filling tanks with fuel and oil are mostly located in the forward portion of the chain saw main body and the presence of the sensing lever means in this portion of the chain saw presents an obstacle.